Present telecommunication system technology includes a wide variety of wireless networking systems associated with both voice and data communications. An overview of several of these wireless networking systems is presented by Amitava Dutta-Roy, Communications Networks for Homes, IEEE Spectrum, pg. 26, December 1999. Therein, Dutta-Roy discusses several communication protocols in the 2.4 GHz band, including IEEE 802.11 direct-sequence spread spectrum (DSSS) and frequency-hopping (FHSS) protocols. A disadvantage of these protocols is the high overhead associated with their implementation. A less complex wireless protocol known as Shared Wireless Access Protocol (SWAP) also operates in the 2.4 GHz band. This protocol has been developed by the HomeRF Working Group and is supported by North American communications companies. The SWAP protocol uses frequency-hopping spread spectrum technology to produce a data rate of 1 Mb/sec. Another less complex protocol is named Bluetooth after a 10th century Scandinavian king who united several Danish kingdoms. This protocol also operates in the 2.4 GHz band and advantageously offers short-range wireless communication between Bluetooth devices without the need for a central network.
The Bluetooth protocol provides a 1 Mb/sec data rate with low energy consumption for battery powered devices operating in the 2.4 GHz ISM (industrial, scientific, medical) band. The current Bluetooth protocol provides a 10-meter range and an asymmetric data transfer rate of 721 kb/sec. The protocol supports a maximum of three voice channels for synchronous, CVSD-encoded transmission at 64 kb/sec. The Bluetooth protocol treats all radios as peer units except for a unique 48-bit address. At the start of any connection, the initiating unit is a temporary master. This temporary assignment, however, may change after initial communications are established. Each master may have active connections of up to seven slaves. Such a connection between a master and one or more slaves forms a “piconet.” Link management allows communication between piconets, thereby forming “scattemets.” Typical Bluetooth master devices include cordless phone base stations, local area network (LAN) access points, laptop computers, or bridges to other networks. Bluetooth slave devices may include cordless handsets, cell phones, headsets, personal digital assistants, digital cameras, or computer peripherals such as printers, scanners, fax machines and other devices.
The Bluetooth protocol uses time-division duplex (TDD) to support bi-directional communication. Spread-spectrum technology or frequency diversity with frequency hopping permits operation in noisy environments and permits multiple piconets to exist in close proximity. The frequency hopping scheme permits up to 1600 hops per second over 79 1-MHZ channels or the entire ISM spectrum. Various error correcting schemes permit data packet protection by ⅓ and ⅔ rate forward error correction. Further, Bluetooth uses retransmission of packets for guaranteed reliability. These schemes help correct data errors, but at the expense of throughput.
The Bluetooth protocol is specified in detail in Specification of the Bluetooth System, Version 1.0A, Jul. 26, 1999, which is incorporated herein by reference.
In some Bluetooth applications, the master could be an access point (AP) which can afford to transmit at, for example, a 20 dBm power level, while the slave could be a mobile unit with strict power consumption limitations that permit it to transmit only at a substantially lower power level, for example 0 dBm. One conventional example of such a communications system is a cordless telephone system wherein the master is the base unit and the slaves are the mobile phone units. In the exemplary system specified above, there would be an imbalance between the master-to-slave link (i.e., the downlink) and the slave-to-master links (i.e., the uplinks). Considering now a voice application such as the aforementioned cordless telephone system, even when using a receive diversity antenna at the master, such a system would achieve a 10 dB diversity gain with selection diversity. Thus, there would still be a 10 dB power imbalance between the downlink and the uplink transmissions. This situation is illustrated in FIG. 1.
The example of FIG. 1 assumes no retransmissions in either direction, because it is typically desired to conserve power consumption both for reception and transmission at the slave. Also, if the master employs some form of transmission diversity, this would further increase the imbalance between uplink and downlink.
It is desirable in view of the foregoing to compensate for power imbalances such as described above, in order to balance the uplink and downlink.
According to the present invention, the uplink slave-to-master transmission frequency can be dynamically selected from a plurality of previous downlink master-to-slave transmission frequencies based on quality measures thereof, which produces improved uplink performance and thereby advantageously reduces imbalances between the uplink and downlink.